In the title mol-ecule, C(18)H(18)O(5), the two aromatic rings are connected by a flexible 3-oxapentane chain. The mol-ecule has a crystallographic twofold rotation axis (C(2)) passing through the central O atom. An intra-molecular C-H⋯O hydrogen bond is observed in the solid state.

The crystal structure of the title compound C(8)H(10)N(3) (+)·ClO(4) (-)·C(12)H(24)O(6)·H(2)O, consists of an organic (1H-benzimidazol-2-yl)methanaminium cation, an inorganic ClO(4) (-) anion, one 18-crown-6 mol-ecule and one water mol-ecule. In the crystal, the cations and 18-crown-6 mol-ecules are linked by N-H⋯O hydrogen bonds. The crystal packing is stabilized by inter-molecular O-H⋯O, O-H⋯...

In the title mol-ecule, C(18)H(18)N(2)O(2), the bicyclic ring system and the benzene ring form a dihedral angle of 13.45 (3)°. In the crystal structure, weak inter-molecular C-H⋯O hydrogen bonds link mol-ecules into chains propagated along [201].

In the mol-ecule of the title compound, C(18)H(18)N(4)O(2), the aromatic rings are oriented at a dihedral angle of 3.72 (3)°. In the crystal structure, inter-molecular C-H⋯O hydrogen bonds link the mol-ecules into centrosymmetric dimers. There are also C-H⋯π inter-actions.

In the title mol-ecule, C(18)H(18)F(2)N(2)O(3)S, the dihedral angle between the benzene rings is 79.40 (11)°. The 2,4-difluoro-benzyl and azetidine fragments adopt a trans arrangement relative to the central benzene ring. In the crystal, weak C-H⋯O hydrogen bonds connect mol-ecules into a two-dimensional network parallel to (001).

In the crystal of the title compound, 2CH(6)N(3) (+)·C(10)H(6)O(6)S(2) (2-)·C(12)H(24)O(6), the 1,5-naphthnalenedisulfonate anion and the 18-crown-6 mol-ecule lie across inversion centers. The guanidin-ium cation links with the 1,5-naphthnalenedisulfonate anion and 18-crown-6 mol-ecule via N-H⋯O hydrogen bonds.

The title compound, C(18)H(18)O(2), which exhibits blue emission in the solid state, is an inter-mediate in the preparation of liquid crystals and polymers. The mol-ecule is located on an inversion centre. In the crystal, mol-ecules are arranged in a herringbone motif.

In the crystal of the title compound, 2CH(6)N(3) (+)·2Cl(-)·C(12)H(24)O(6), the 18-crown-6 mol-ecule is located across an inversion center. The guanidinium cation links to the 18-crown-6 mol-ecule and chloride anion via N-H⋯O and N-H⋯Cl hydrogen bonds.

The title compound, C(18)H(16)N(2), crystallizes with one and a half independent mol-ecules in the asymmetric unit, with the half-mol-ecule being completed by crystallographic inversion symmetry. Both independent mol-ecules are almost planar, with the non-H atoms exhibiting r.m.s. deviations from the least-squares mol-ecular plane of 0.175 and 0.118 Å, respectively.

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